Vacuum degasifying apparatus with electromagnetic stirring means



1969 TAKAHO KAWAWA ETAL 3,

VACUUM DEGASIFYING APPARATUS WITH ELECTROMAGNETIC STIRRING MEANS Filed Dec. 23, 1966 Sheet I of 2 3 FIG. I

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VACUUM DEGASIFYING APPARATUS WITH ELECTROMAGNETIC STIRRING MEANS Filed Dec. 23, 1966 Sheet & of2

FIG. I 3

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United States Patent.

3 452 973 VACUUM DEGASIFYING APPARATUS WITH ELECTROMAGNETIC STIRRING MEANS Takaho Kawawa, Tokyo, and Masuta Okubo, Yokohamashi, Japan, assignors to Nippon Kokan Kabushiki Kaisha, Tokyo, Japan, a corporation of Japan Filed Dec. 23, 1966, Ser. No. 604,470 Claims priority, application Japan, Dec. 29, 1965, 40/ 80,963 Int. Cl. C21c 7/00; HOSb /14 US. Cl. 266-34 3 Claims A vacuum degasifying apparatus for removing gases deteriorating the desired metallic structure of a product and contained in raw molten metal. The removal of the gases is effectively advanced by a stirring means acting also as a temperature compensating means and an annular vacuum vessel for containing molten metal. The stirring means is a mangetic circuit for producing an alternating low frequency magnetic flux and maintaining the molten metal at a predetermined temperature, whereby the molten metal experiences electromagnetic force to be stirred up and in addition its temperature can be compensated by Joule heat generated in the molten metal due to an electric current induced therein.

The present invention relates to vacuum degasifying apparatus for removing gases deteriorating the desired metallic structure of the product and contained in the raw molten metal, and more particularly, to vacuum degasifying apparatus where the degasifying treatment is made by forcibly stirring molten metal in an evacuated degasifying vessel.

In order to enhance the efiiciency of degasification, it is desirable to stir well molten metal in the evacuated vessel to expose the former to the vacuum sufliciently. It is further necessary to provide a suitable temperature compensating means to avoid temperature fall of the molten metal after degasification.

To separately provide a molten metal stirring means and a temperature compensating means, however, leads to the complexity of the entire apparatus and hence high costs to the advantage. Although means for stirring molten metal in the furnace by means of induced current at low frequencies of the order of below 20 cycles per second is known in the art, it is too complex and expensive to be used for stirring molten metal in the aforementioned evacuated vessel.

The invention is intended in view of the above technical difiiculties and has its object to provide a vacuum degasifying apparatus comprising an annular vacuum vessel to contain molten metal in an annular fashion so as to form a closed circulation path for molten metal and a magnetic circuit a portion of which penetrates through the closed circulation path to produce an alternating low frequency magnetic flux which links with the closed circulation path. With this arrangement, molten metal in the annular vacuum vessel experiences electromagnetic force due to the alternating low frequency magnetic flux set up in the closed magnetic circuit linking with the closed circulation path when power source is on, so that it is moved in a given direction to be stirred up, while at the same time decrease in temperature of molten metal owing to the degasification is compensated by Joule heat generated in the molten metal due to electric current induced therein, thereby maintaining the molten metal at a predetermined temperature.

It is desirable, if possible in practice, to make use of the commercial power source (50 to 60 c./s.) in order to have the magnetic circuit effectively achieve the two-fold function; namely, the sufficient stirring of molten metal and the temperature compensation. When the commercial power source is used, a frequency converter which is necessary in using a high frequency induction heating furnace 3,452,973 Patented July 1, 1969 or in stirring molten metal in the furnace by means of an AC. source with a frequency lower than the frequency of the commercial power source, is not required, so that the equipment is greatly simplified and appropriate stirring and temperature compensation may be made.

The stirring and heating of molten metal may be more effectively made with a vacuum degasifying vessel having such a configuration that a circulation path having different cross sections is formed, rather than with a completely doughnut-like vessel, as the difference in cross sections of the circulation path gives rise to disturbance of flow of molten metal.

The invention is now described in conjunction with preferred embodiment thereof with reference to the accompanying drawing, in which:

FIG. 1 is a cross sectional view illustrating one embodiment of the vacuum degasifying apparatus according to this invention;

FIG. 2 is a section taken along line II-JI of FIG. 1; and

FIG. 3 is a cross sectional view illustrating another embodiment of the vacuum degasifying apparatus according to this invention.

Referring to the drawing, and particularly to FIGS. 1 and 2, an exemplary vacuum degasifying apparatus comprises a vacuum vessel 1 and a magnetic circuit 2. The vacuum vessel 1, as is seen from FIG. 2, has an annular configuration having an oval outer side wall and a circular inner side wall. The vessel 1 communicates at its ceiling with a supply conduit 4 leading to a ladle 3 containing molten metal indicated at a to be degasified, and is also provided at its ceiling with an exhause port 5 for connection of an evacuating pump not shown. The bottom of the vessel 1 communicates with a discharge conduit 6 for discharging degasified molten metal indicated at b. The discharge conduit 6 extends vertically downwardly with its lower end being open within a turn dish 7 for continuous molding and containing already degasified molten metal. The turndish 7 is provided at its bottom with a pouring orifice 8 which is closed and unclosed by a valve means 9.

-In the central space penetrating the annular vacuum vessel 1 is disposed vertically a portion of an iron core 10 constituting the magnetic circuit 2. Around the core 10 is provided an insulating layer around which is wound a conductor coil 11 which also serves as a conduit for cooling water. When an alternating voltage is applied across the coil 11, an alternating magnetic flux is produced in the core 10. A coil 12 surrounding the exhaust conduit 6 serves for auxiliary induction heating molten metal passing through the exhaust conduit 6 thereby compensating the temperature of molten metal to a constant value.

In operation, molten metal is supplied into the vacuum vessel 1 from the ladle 3, and concurrently with the commencement of the degasifying process by driving the evacuating pump a low frequency current from the commercial power source is passed through the coil 11 wound on the core 10' to produce a low frequency magnetic flux in the core 10, thereby exercising electromagnetic force in a given direction to the molten metal in the circulation path formed by the vacuum vessel 1 to cause molten metal to start moving. The flow of molten metal is disturbed because the circulation path has different cross sections having the same depth and different widths, so that effective stirring of molten metal may be made. The establishment of low frequency alternating magnetic flux, on the other hand, gives rise to the generation of Joule heat due to the induced current. Thus, the decrease of the molten metal temperature resulting from the degasification of molten metal is compensated by the Joule heat. As the specific weight of the degasified portion of molten metal is greater than that of the undegasified portion, the molten metal contained in the vacuum vessel is subject to a vertical convection, so that the degasified portion of molten metal tends to settle on the bottom of the vacuum vessel 1. Consequently, the degasified molten metal flows through the exhaust conduit 6 down into the turndish 7 for the continuous molding. Since the difference between the level of the free surface of the molten metal contained in the vacuum vessel 1 and the level of the free surface of the molten metal contained in the turndish 7 is maintained to a predetermined constant value depending upon the degree of vacuum within the vacuum vessel 1, there is no need of providing a valve at the discharge conduit 6. Also the level of the molten metal in the vacuum vessel may be known from a measurement of the degree of vacuum within the vacuum vessel 1.

The embodiment shown in FIG. 3 is somewhat different from the previous embodiment in the constructional standpoint. In this embodiment the supply conduit 104 leading to the ladle 103 is in communication with the vacuum vessel 101 at the bottom thereof. Further, the portion of the ceiling of the vacuum vessel 101 opposing the opening of the supply conduit 104 is extended as indicated at 113. This extension or raising of a portion of the ceiling is down since when the opening of the supply conduit is provided at the bottom of the vacuum vessel the molten metal which has been in balance with respect to the atmospheric pressure when in the ladle, upon entering the vacuum vessel 101, raves about considerably.

The foregoing embodiments are intended by taking the continuous molding into consideration, so that it is necessary to assure uninterrupted flow of molten metal over the entire continuous molding process by balancing the quantity of molten metal supplied from the ladle to the vacuum vessel and the quantity of molten metal supplied from the vacuum vessel to the turndish and then to the subsequent mold not shown. When separate moldings are to be made, the degasified molten metal in the turndish 7 may, of course, be poured into individual molds.

It is to be understood that the foregoing description of specific examples of this invention is made by way of example only and is not to be considered as a limitation on its scope.

What is claimed is:

1. A vacuum degasifying apparatus comprising a vacuum vessel in communication with :a supply conduit for supplying molten metal to be degasified, an exhaust port leading to an evacuating means for degasification and with a discharge conduit for discharging molten metal into a turndish, and means for stirring molten metal in said vacuum vessel as well as compensating decrease in temperature of molten metal after degasification, charac terized in that said vacuum vessel has an annular configuration so as to form a closed circulation path of molten metal contained therein, and that said means is a magnetic circuit a portion of which vertically penetrates the substantial center of said closed circulation path so as to produce a low frequency alternating magnetic flux which links with said closed circulation path.

2. A vacuum degasifying apparatus as claimed in claim 1 wherein said low frequency alternating magnetic flux is produced by a current supplied from a commercial A.C. source at or cycle per second.

3. A vacuum degasifying apparatus as claimed in claim 1 wherein said closed circulation path has different cross sections.

References Cited UNITED STATES PATENTS 994,022 5/1911 McNitt 1328 1,675,237 6/1928 Unger 1328 2,513,082 6/1950 Dreyfus 266-34 3,215,424 11/1965 Kanamori 26634 3,235,243 2/1966- Taylor 26634 3,352,665 11/1967 Stenkvist et al. 266-34 3,384,362 5/1968 Philbrick 26634 FOREIGN PATENTS 263,856 7/1927 Great Britain.

J. SPENCER OVERHOLSER, Primary Examiner.

EUGENE MAR, Assistant Examiner.

US. Cl. X.R. 1328; 259-4 

1. A VACUUM DEGASIFYING APPARATUS COMPRISING A VACUUM VESSEL IN COMMUNICATION WITH A SUPPLY CONDUIT FOR SUPPLYING MOLTEN METAL TO BE DEGASIFIED, AN EXHAUST PORT LEADING TO AN EVACUATING MEANS FOR DEGASIFICATION AND WITH A DISCHARGE CONDUIT FOR DESCHARGING MOLTEN METAL INTO A TURNDISH, AND MEANS FOR STIRRING MOLTEN METAL IN SAID VACUUM VESSEL AS WELL AS COMPENSATING DECREASE IN TEMPERATURE OF MOLTEN METAL AFTER DEGASIFICATION, CHARACTERIZED IN THAT SAID VACUUM VESSEL HAS AN ANNULAR CONFIGURATION SO AS TO FORM A CLOSED CIRCULATION PATH OF MOLTEN METAL CONTAINED THEREIN, AND THAT SAID MEANS IS A MAGNETIC CIRCUIT A PORTION OF WHICH VERTICALLY PENETRATES THE SUBSTANTIAL CENTER OF SAID CLOSED CIRCULATION PATH SO AS TO PRODUCE A LOW FREQUENCY ALTERNATING MAGNETIC FLUX WHICH LINKS WITH SAID CLOSED CIRCULATION PATH. 